/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.config;

import java.lang.reflect.Constructor;

import org.springframework.beans.BeansException;
import org.springframework.lang.Nullable;

/**
 * Extension of the {@link InstantiationAwareBeanPostProcessor} interface,
 * adding a callback for predicting the eventual type of a processed bean.
 *
 * <p><b>NOTE:</b> This interface is a special purpose interface, mainly for
 * internal use within the framework. In general, application-provided
 * post-processors should simply implement the plain {@link BeanPostProcessor}
 * interface or derive from the {@link InstantiationAwareBeanPostProcessorAdapter}
 * class. New methods might be added to this interface even in point releases.
 *
 * @author Juergen Hoeller
 * @since 2.0.3
 * @see InstantiationAwareBeanPostProcessorAdapter
 */

/**
 1. 作用总结
 类型预测：通过 predictBeanType 方法在 Bean 创建前预测其最终类型，优化类型检查和依赖解析
 构造函数选择：通过 determineCandidateConstructors 方法支持构造函数自动装配和自定义构造函数选择逻辑
 循环依赖解决：通过 getEarlyBeanReference 方法提供早期引用，解决 Bean 间的循环依赖问题

 2. 内部成员解释
 predictBeanType(Class<?> beanClass, String beanName)：预测通过 postProcessBeforeInstantiation 回调最终返回的 Bean 类型，在 Bean 实际创建之前预测其类型，用于优化类型检查和依赖解析
 determineCandidateConstructors(Class<?> beanClass, String beanName)：确定给定 Bean 的候选构造函数，允许自定义构造函数选择逻辑，支持基于注解的构造函数自动装配
 getEarlyBeanReference(Object bean, String beanName)：获取指定 Bean 的早期访问引用，通常用于解决循环依赖，在目标 Bean 实例完全初始化之前提供包装器

 3. 与其他类和接口的关系
	 BeanPostProcessor
	 ↑
	 InstantiationAwareBeanPostProcessor
	 ↑
	 SmartInstantiationAwareBeanPostProcessor (当前接口)
	 ↑
	 AbstractAutoProxyCreator (重要实现类)
	 ↑
	 InfrastructureAdvisorAutoProxyCreator
	 AspectJAwareAdvisorAutoProxyCreator
	 AnnotationAwareAspectJAutoProxyCreator (AOP代理核心实现)
 主要关系说明：
	 SmartInstantiationAwareBeanPostProcessor 继承自 InstantiationAwareBeanPostProcessor，扩展了其功能
	 InstantiationAwareBeanPostProcessor 又继承自 BeanPostProcessor，形成完整的后处理器层次结构
	 核心实现类是 AbstractAutoProxyCreator 及其子类，用于实现 AOP 代理功能
	 AnnotationAwareAspectJAutoProxyCreator 是最重要的实现类，负责处理基于注解的 AOP 代理

 4. 使用场景和实际应用示例
 主要使用场景：
	 AOP 代理创建：Spring AOP 通过 AbstractAutoProxyCreator 实现该接口来创建代理对象
	 循环依赖解决：通过 getEarlyBeanReference 方法提供早期引用解决循环依赖
	 构造函数自动装配：通过 determineCandidateConstructors 方法支持基于注解的构造函数注入
	 类型预测优化：通过 predictBeanType 方法优化类型检查和依赖解析




 */
public interface SmartInstantiationAwareBeanPostProcessor extends InstantiationAwareBeanPostProcessor {

	/**
	 * Predict the type of the bean to be eventually returned from this
	 * processor's {@link #postProcessBeforeInstantiation} callback.
	 * <p>The default implementation returns {@code null}.
	 * @param beanClass the raw class of the bean
	 * @param beanName the name of the bean
	 * @return the type of the bean, or {@code null} if not predictable
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	/**
	 作用：预测通过 postProcessBeforeInstantiation 回调最终返回的Bean类型。
	 在Bean实际创建之前预测其类型
	 用于优化类型检查和依赖解析
	 返回 null 表示无法预测类型
	 */
	@Nullable
	default Class<?> predictBeanType(Class<?> beanClass, String beanName) throws BeansException {
		return null;
	}

	/**
	 * Determine the candidate constructors to use for the given bean.
	 * <p>The default implementation returns {@code null}.
	 * @param beanClass the raw class of the bean (never {@code null})
	 * @param beanName the name of the bean
	 * @return the candidate constructors, or {@code null} if none specified
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	/**
	 作用：确定给定Bean的候选构造函数。
	 关键特性：
	 允许自定义构造函数选择逻辑
	 支持基于注解的构造函数自动装配（如 @Autowired）
	 返回 null 表示使用默认构造函数解析逻辑
	 */
	@Nullable
	default Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName)
			throws BeansException {

		return null;
	}

	/**
	 * Obtain a reference for early access to the specified bean,
	 * typically for the purpose of resolving a circular reference.
	 * <p>This callback gives post-processors a chance to expose a wrapper
	 * early - that is, before the target bean instance is fully initialized.
	 * The exposed object should be equivalent to the what
	 * {@link #postProcessBeforeInitialization} / {@link #postProcessAfterInitialization}
	 * would expose otherwise. Note that the object returned by this method will
	 * be used as bean reference unless the post-processor returns a different
	 * wrapper from said post-process callbacks. In other words: Those post-process
	 * callbacks may either eventually expose the same reference or alternatively
	 * return the raw bean instance from those subsequent callbacks (if the wrapper
	 * for the affected bean has been built for a call to this method already,
	 * it will be exposes as final bean reference by default).
	 * <p>The default implementation returns the given {@code bean} as-is.
	 * @param bean the raw bean instance
	 * @param beanName the name of the bean
	 * @return the object to expose as bean reference
	 * (typically with the passed-in bean instance as default)
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	/**
	 作用：获取指定Bean的早期访问引用，通常用于解决循环依赖。
	 关键特性：
	 在目标Bean实例完全初始化之前提供包装器
	 解决循环依赖问题的关键机制
	 返回的对象应等效于 postProcessBeforeInitialization / postProcessAfterInitialization 暴露的对象
	 */
	default Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
		return bean;
	}

}
